The large majority of cancers in the United States initiate from epithelial cells. In these epithelial cancers the major clinical problem is metastasis. A major unsolved challenge is determining which of the many cell epithelial cell types are most important to the tumor's ability to invade, metastasize, and resist therapy. Most efforts to classify the relative ability of cancer cells to initiate tumors or to metastasize to distant sites rely on sorting the cells based on cell surface markers prior to analysis. The sorting can be accomplished by Fluorescence Activated Cell Sorting (FACS) or by Magnetic Activated Cell Sorting (MACS). However, in either case the researcher needs to decide in advance how to identify the cell population to be tested and cell populations can only be compared that both survive the sorting process and for which reliable cell surface markers or other fluorescent reporters can be developed. Accordingly, these approaches may fail to identify the cancer cell subpopulations that are actually driving the functional properties of the tumor.